Exposure to stress is known to have adverse effects on the cardiovascular (CV) health in humans and in experimental animals. However, the nature of stress is not well understood, and there is a need to investigate how individual differences in stress susceptibility may influence CV response to naturalistic or social stressors. The proposed work will investigate different elements of social stress on CV response in adult, male laboratory rats of three inbred strains (Spontaneously Hypertensive Rat, and the Maudsley Reactive & Nonreactive Rats) which are stress-sensitive or stress resistant, and differ in their susceptibility to develop hypertension. CV response will be assessed by measuring mean arterial blood pressure (BP), systolic BP, diastolic BP, heart rate (HR), and pulse pressure (PP) of rats via arterial cannulation of the abdominal aorta. An established method of recording these variables before, during, and after stress exposures using a computer program will be central to all of the proposed experiments. Four studies will address five major questions: (1) the effects of repeated defeat on acute CV response; (2) the effects of establishing territory or social control through fighting on CV response; (3) the influence of prior aggressive experience on CV response to various social stress contexts; (4) the effect of exposure to chronic stress stimuli on subsequent CV response to an acute stressor; and (5) the nature of prior social role within an established social group on CV response to stressful social confrontations with familiar colony mates of different social status. In this latter study we will initiate investigations into female social behavior and CV response to social stimuli. These studies will, as a whole, provide an important foundation for the understanding of how naturalistic stressors influence CV function in laboratory rats and an excellent forum for training students in the psychobiology of hypertension.